1. Field of the Invention
The present invention relates to a key telephone system with cordless terminals in a private branch exchange that includes a switching unit, stationary key terminals, and at least one of mobile cordless and GSM terminals. The switching unit is adapted to switch calls to the stationary key terminals and to the at least one of the mobile cordless and GSM terminals. The system also includes a first trunk group and a key server system, in which the stationary key terminals are coupled to the switching unit through the first trunk group and the key server system.
2. Discussion of Background Information
Apart from simple telephone installations that are connected to a single connection line, there are terminals which, with a talking key, have access to several lines via an additional control panel. With the appropriate connection of numerous such special terminals, numerous systems arise, which, for example, are characterized as executive-secretary, key, key telephone, or broker systems. Three main examples for application of such systems are described in Ohmann, F.: Kommunikations-Endgerate, Springer-Verlag, Berlin 1983, chapter 4.2.7, pages 187-193:
hierarchically structured work group, PA1 work group with a team structure, and PA1 central operator to fill in for absentee professionals. PA1 In accordance with another feature of the present invention, the additional server includes a memory unit. The memory unit is adapted to store information about the associated specified lines of the second trunk group and each at least one additional terminal. PA1 In accordance with still another feature of the present invention, the additional server includes a switch device to terminate to the at least one additional terminal. Further, the additional server further includes a memory unit that is adapted to store information about the associated specified lines of the second trunk group and each at least one additional terminal. Still further, the switch device is coupled to the memory unit.
Broker and commissioner systems are particularly important, in which, with reference to external calls, each member of a work group can fill in for every other team member and take his calls. For this, several joint switched lines are led to many terminals. External calls are therefore signaled simultaneously at numerous terminals, so that various team members can take an incoming call.
It is known, for example, that cordless telephone systems that operate in accordance with DECT or GSM standards allow the subscriber to conduct conversations independent of his work station. In EP 0 533 510 A2, a cordless telephone system with key functionality is described, the cordless telephones of which exhibit control keys and indicators, each of which are assigned to a switched line. Furthermore, a register is provided, which contains data concerning the switched lines that are assigned to the cordless telephone. The known cordless key telephone system exhibits the essential performance features of known key telephone systems. As the calling signal is received, the cordless telephone thus tests whether the line linked to the calling signal is assigned to the cordless telephone in question. If this is the case, the call is shown on the display, whereafter the subscriber can take the call by tapping the pertinent key.
The known cordless key telephone system thus exhibits special cordless telephones that require an additional keyboard, an additional register area, as well as the corresponding operations software, and thus they are comparatively expensive. Conventional cordless telephones without key functionality, however, cannot be used. On the other hand, the possibility provided for the subscriber to take calls selectively from various lines is of lesser importance.